Allow promotion conditions to work with in-memory line items, improve performance

[mamhoff]

Summary

This PR does four things:

1. Fix the DistributedAmountsHandler to not require line items IDs, so it can work with in-memory line items
2. Fix the taxon condition to work with in-memory line items (by not executing an ActiveRecord query on line items).
3. For the taxon family of conditions, reduces the number of calls to the database to find the preconfigured taxon IDs and children needed to check against to one per condition per promotion run.
4. For the option value condition, do not use pluck and rather take advantage of loaded option values.

The taxon condition is likely one of our most-used conditions, so it makes sense to spend a bit of time here making sure it's not too slow.

Checklist

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[codecov]

Codecov Report

❌ Patch coverage is 96.15385% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 89.46%. Comparing base (57e8ef9) to head (18fd749).
⚠️ Report is 6 commits behind head on main.

Files with missing lines	Patch %	Lines
...s/solidus_promotions/conditions/taxon_condition.rb	90.90%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6383      +/-   ##
==========================================
- Coverage   89.46%   89.46%   -0.01%     
==========================================
  Files         977      977              
  Lines       20386    20394       +8     
==========================================
+ Hits        18238    18245       +7     
- Misses       2148     2149       +1     

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[tvdeyen]

Great stuff. I think the funky SQL is worth the benefit.